Duplicating process



transfer of a suflicient quantity of ink would Patented July 11, 1933 UNITED STATES PATENT OFFICE KENNETH C. D. HICKMAN, OF ROCHESTER, NEW YORK, ASSIGNOR TO EASTMAN KODAK COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK ionrmca'rme PROCESS No Drawing.

This invention relates toduplicating processes of the kind in which typing, writing or any design is formed on a sheet of paper in a special ink, this writing or design being then transferred to a suitable pad, and duplicate copies being made by pressing other sheets of paper against the impression on the pad. For such a process special inks are employed but the number of satisfactory copies obtained is limited by the fact that the transfer ink is soon removed from the pad. In prior processes of this kind, also, duplicate copies as reproduced are not as intense as the original, and as more and more copies are taken off, the ink becomes fainter.

The present invention contemplates the use of a new principle in such a duplicating process. It comprises having in the duplicating paper material capable of giving a good black except for one constituent, which constituent is supplied by the writing transferred to the pad. This constituent is a sensitizer, activator, 0r catalyst for a darkening reaction which the substance in the paper undergoes. Under these conditions a relatively large number of copies can be obtained since only the smallest traces of this type of constituent are required to darken the paper. Such small traces will be readily transferred f; cm the pad to the paper long after the no longer occur.

My invention may be carried out in a large number of ways and with a variety of materials, some of which have been only recently discovered. Certain definite ways of carrying out the invention are given by way of example only.

In. all of the following examples we will assume for the sake of illustration that we employ a simple hectograph machine in which after writing, typing or drawing on paper with a special ink, this ink may then be transferred to a moistened pad made of slightly hardened gelatin or the like, and sheets of paper for duplicates are pressed firmly one by one against the impression on this pad.

- A simple method of carrying out the invention will be to make the original writing,

Application filed July 13, 1932. Serial No. 622,325.

drawing or typing with an ink containing thioacetamide. Such an ink would comprise a vehicle, thioacetamide, and a dye to make the writing visible The duplicating paper is one coated with a relatively insensitive silver bromide emulsion. In a machine of the kind described, traces of the thioacetamide which had been transferred to the pad would, in turn, be transferred to the duplicating paper. be developed in a photographic developer and will give a good black only where the writing or design had been impressed.

In further illustrations, for the sake of simplicity, I will refer to the typing, writing or drawing of the original as the design. I shall also refer to the paper on which the final copies are made as the duplicating paper.

A more useful method of carrying out the invention is as follows:

Example I The ink used for the original design contalns thiourea or an equivalent sulphur-containing body in concentrated watery solution together with a little glue or glycerin or other vehicle and sufficient coloring matter to make it visible during writing.

suitable formula for such an ink will be Formula 1 I Parts Thiourea 10 Glue Glycerine Methylene blue Water 100 .of machine is preferable.

The duplicating paper has on its surface an emulsion of mercurous oxalate or within The duplicating paper can- Formula 2 Part Gelatin, 15% aqueous solution Potassium oxalate, 2.5% solution 1 Mercurous nitrate, 6.5% aqueous solution contalning about 7% conc. nitric acid 1 This emulsionis made by adding the potassium oxalate solution to the gelatin solution, and then adding the mercurous nitrate solution with vigorous mechanical stirring.

A mercurous oxalate may be made by precipitation and incorporated in the fibers of the paper in a manner which is well known. Thus a lightly sized paper may be moistened with a solution of mercurous nitrate (5%) in dilute nitric acid and then after partial or complete drying may be moistened with 2% potassium oxalate solution and dried before use. Duplicating papers made in either way will be satisfactory for duplicating purposes. When these duplicating papers are pressed into contact with the transfer pad, they pick up sufiicient thiourea to cause partial darkening in the places occupied by the design. This darkening may be further enhanced by passing a hot iron over the oxalate paper. Where large numbers of duplicates are to be made, it will be most convenient to have a heated roll over which the copies are passed as they are made.

Example I I The ink used is the same as that given under Example I; that is, one containing thiourea.

The duplicating paper has on its surface a layer containing silver oxalate. A suitable emulsion may be made by mixing the following ingredients:

Formula 3 Part Gelatin, 15% aqueous solution 1 Potassium oxalate, 3% solution 1 Silver nitrate, 5.2 solution 1 This emulsion is made by first adding the potassium oxalate to the gelatin solution and then adding the silver nitrate with constant mechanical stirring. After this gelatin-silver oxalate emulsion is prepared, it is coated on the paper, chilled, dried, and preserved in the dark until ready for use.

As before, the design is madein the ink containing thiourea and this ink is pressed into contact with the transfer pad. The duplicating paper is then used as indicated to pick up the design in traces of thiourea from the pad. The paper becomes darkened at the points where the design is located. In this heated roll.

Example [[1 In this case a somewhat different combination of ink and darkening substance is used. The paper contains a mixture of lead trichloroacetate and thioacetamide, in faintly acid environment. Under these conditions the sulphur ion in the thioacetamide and the lead do not unite readily. To promote the darkening I use an ink containing an alkali. The small traces of alkali which are transferred to the pad and then to the duplicating paper are sufficient to promote the darkening reaction and give a good black.

The ink, for example, may contain glue, glycerin, orother suitable vehicle together with sodium hydroxide and sufficient coloring matter to make it visible during writing.

The duplicating paper may have on its surface a thin coating containing a mixture of lead trichloroacetate and thioacetamide or may have simply been passed through a solution containing these substances. For a coating material the following will be satisfactory:

Form/dart Grams Thioacetamide Lead trichloracetate 17 Acetic acid-glacial 0.5 Water 100 The process is carried out exactly as before. The ink in this case serves to promote the darkening reaction by providing the slightly alkaline environment necessary.

There are several other types of reaction which, it will appear to those skilled in the art, may be made use of in this process. Any substance which will sensitize, activate, or catalyze a darkening reaction between other constituents will serve as an ink'if the corresponding substances which are so activated or catalyzed are used in the paper. The type of darkening reaction which I have described consists of a reaction between the metal ion ofa salt of a heavy metal and the sulphide ion of a sulphur-containing body. As is well known, this type of reaction occurs between the ions of such metals as silver, lead, and mercury, and any one of a large group of organic and inorganic substances capable of furnishing the sulphide ion. A number of other metals such as nickel, manganese, and others, also form sulphides of varying color. Some of the metal sulphides are too light in color to be of practical use in my invention. I prefer, for obvious reasons, to use the salts of the metals which give dark colored sulphides, since these will naturally give the most intense copies.

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It will also naturally follow that the darkening reaction will be more easily activated, catalyzed, or sensitized in some cases than in others. It follows that the largest number of good duplicates can be made by employing a reaction which is easily promoted by extremely small quantities of some constituent present in the ink.

If a reaction involving the formation of a dark colored metal sulphide is involved, I may employ any one of alarge group of substances which are capable of furnishing the sulphide ion. While certain inorganic sub-\ stances like sodium sulphide may .be' employed, I prefer to use such organic sulphurcontaining bodies as thiourea or thioacetanamide which are as satisfactory as any.

As already stated, I may use also for the constituent of the ink an alkali which will promote the formation of sulphide from a heavy metal salt and a sulphur-containing body, which reaction takes place only in a slightly alkaline environment. For this purpose I may use any strongly alkaline substance but the nonvolatile, strong alkalies, such as sodium hydroxide or potassium hydroxide, will be most satisfactory.

Another type of reaction which may be employed in carrying out my invention is where the darkening constituent of the ink is the more soluble, less bulky constituent of a binary mixture. Thus an ink containing thiourea or thioacetamide may be used to darken by transference a paper coated with a simple salt of a metallic sulphide, such salt being incapable of darkening by itself, even with the aplication of heat (thus differing from the oxalate examples). Thus a paper coated with basic lead acetate or lead chloride can be darkened with a transferred thiourea or thioacetamide ink.

I contemplate as included within my invention the'making' of duplicates in the manner indicated by employing a paper containing any substance or substances capable of undergoing a darkening reaction except for one constituent, which constituent is supplied by the ink. It will be evident that many such combinations exist and that many variations are possible.

I claim:

1. A duplicating process that comprises forming a design on paper with an ink, transferring impressions of said design to a suitable pad, and then pressing a sheet of paper against the impression on said pad, said second paper containing a substance which becomes darkened upon contact with another substance contained in the ink and transferred to the second sheet from the pad.

2. A duplicating process that comprises forming a design on paper with an ink, transferring impressions of said design to a suitable pad, and then pressing a sheet of paper against the impression on said pad, said second paper containing in its fiber a substance which becomes darkened upon contact with small traces of another substance contained in the ink and transferred to the second sheet from the pad.

3. A duplicating process that comprises forming a design on paper with an ink, transferring impressions of said design to a suitable'pad, and then pressing a sheet of paper against the impression on said pad, said second paper containing in its surface a substance which becomes darkened upon contact with small traces of another substance con tained in the ink and transferred to the second sheet from the pad.

4. A duplicating process that comprises forminga design on paper with an ink, transferring impressions of said design to a suitable pad, and then pressing a sheet of paper against the impression on said pad, said second paper being coated with a substance which becomes darkened upon contact with small traces of another substance contained in the ink and transferred to the second sheet from the pad.

5. A duplicating process that comprises forming a design on paper with an ink, trans ferring impressions of said design to a suitable pad, and then pressing a sheet of paper against the impression on said pad, said second paper containing a substance which becomes darkened upon contact with small traces of another substance contained in the ink and transferred to the second sheet from the pad, and then submitting the second paper to the action of heat whereby the darkening is further promoted.

6. A duplicating process that comprises forming a design on paper with an ink, transferring impressions of said design to a suitable pad, and then pressing a sheet of paper against the impression onsaid pad, said second paper containing a salt of a heavy metal which reacts to form a dark colored sulphide upon contact with small traces of a substance capable of yielding sulphide ions -which is contained in the ink and is transferred to the second sheet from the pad.

7. A duplicating process that comprises forming a design on paper with an ink, transferring impressions of said design to a suitable pad, pressing a sheet of paper against the impression on said pad, and then submitting the resulting duplicate to the action of heat, said second paper containing a salt 0 a heavy metal which reacts to form a dark colored sulphide upon contact with small traces of a substance capable of yielding sulphide ions which is contained in the ink and is transferred to the second sheet from the ad. p 8. A duplicating process that comprises forming a design on paper with an ink, transferring impressions of said design to a sultable pad, and then pressing a sheet of paper against the impressions on said pad, said second paper containing oxalate of a metal selected from the group comprising lead, silver and mercury and the ink containing a substance capable of yielding sulphide ions, small traces of said ink being transferred to said second paper from the pad.

9. A duplicating process that comprises forming a design on paper with an ink, transferring impressions ofsaid design to a suitable pad, and then pressing a sheet of paper against the impression on said pad, said second paper containing mercurous oxalate and 

